You might find that it's not a problem, so you could try conventional glass before ordering anti-Newton glass. Whether you get Newton's rings will depend on the surface of the film and factors like humidity.

Some AN glass is textured to prevent contact between two smooth surfaces, and some is coated with an anti-reflection coating like that used on lenses to reduce reflections between the two surfaces that are the cause of Newton's rings.

There is a spray, but I believe it is supposed to be sprayed on the negative rather than the glass, and it's messy to clean up. Another such approach I've heard of is to use a dusting of fine talc or cornstarch on the base side of the neg (Newton's rings don't usually form on the emulsion side).

Another source for AN glass is